1. Field of the Invention
The present invention relates to slide parts, each part having a slide surface and more particularly, it relates to slide parts, both base materials of which are made of an aluminum alloy, and to a method for manufacture of the same.
2. Description of the Prior Art
Slide parts which are used in cars or in other vehicles are designed to be lightweight, and therefore, are required to be made of an aluminum alloy. However, aluminum alloys themselves have a defect in that their abrasion-resistance is poor for use in slide parts. In order to overcome this defect, a method of forming an Alumite film layer on the surface of the base metal by anodic oxidation has been described (Machine Planning, Vol. 29, No. 15, pp. 77-86, 1985). This Alumite film layer is effective in improving the abrasion-resistance of the base metal, even though the metal is an aluminum alloy.
It is apparent, that, if both parts of a pair of slide parts are coated with the Alumite film, the abrasion tends to become greater when the parts slide on each other. It has been proven that the abrasion is decreased in the case of a pair of slide parts comprising a part with an Alumite layer, and a part made of steel. Previously, lightweight slide parts have been used comprising an aluminum alloy with an Alumite layer formed thereon by an anodic oxidation treatment as a body side-part and a steel with a high abrasion-resistance or a heat-treated steel as a valve side-part.
However, when the said slide parts are used in a reciprocating system, problems arise, as mentioned below, which result from the variation in the temperature of the lubricants used.
Particularly, since the body side-part (aluminum alloy+Alumite layer) and the valve side part (iron series material) differ in thermal expansion coefficients, the clearance in the slide parts becomes insufficient at low temperatures, which causes sticking (valve slide clearance insufficiency), while the clearance becomes greater at higher temperature, which causes oil leakage. This has been one problem. Further, when the slide parts are used at a high temperature, and then cooled, extraneous substances in the lubricant circuit remain between the valve and the body, which also causes sticking. This has been another problem.
In order to solve these problems, it has been known as a matter of course to use the parts having similar linear expansion coefficients as much as possible in both the body side and the valve side. Therefore, it has been proposed to use an Alumite coated aluminum alloy also at the valve side, and this has already been partly put into practical use. Although the above combination prevents the above-mentioned drawbacks caused by the clearance variations or the like, the problem that the abrasion-resistance is still poor remains, as the Alumite layers are subjected to sliding upon each other.
For the improvement of the abrasion-resistance of aluminum or the like, the following methods are known beside the abovementioned anodic oxidation treatment (Alumite coating treatment).
(1) A method of hardening of the surface by Fe plating. (Refer to Handbook for Metal Plating. Daily Industrial Newspaper Co., 1st Edt., July 25, 1971, page 20)
(2) A method of polishing one aluminum alloy by electrolytic polishing and forming a layer on an aluminum alloy by Fe-P (iron-phosphorus alloy) plating (cf. Japanese Patent Laid-Open Sho No. 58-146763).
(3) A method of etching treatment (hereinafter referred to as "ECM treatment") by electrolytic polishing or chemical polishing on one aluminum alloy and forming a layer containing dispersed particles of SiC (silicon carbide) on the corresponding slide part of aluminum alloy by Fe-P plating (cf. Japanese Patent Laid-Open Sho No. 60-165389).
While these methods have shown some improvements, they are not at all satisfactory. For example, when a high silicon-aluminum alloy (AA Standard: A 390) having a high abrasion-resistance among aluminum alloys is used, the abrasion of other part of Fe-plated material is increased to augment the surface roughness thereof because friction is generated between the primary crystal silicon (Hv 900 to 1100) in the aluminum alloy structure and the other part, whereby both the aluminum alloy itself and the part are noticeably abraded. In addition, when used in the region of high load, the primary crystal silicon cracks or peels off to cause the same phenomenon as in the case of the presence of extraneous substances, whereby the value of baking load is lowered.
Accordingly, the present invention has been so made as to solve the above-mentioned problems, and an object thereof is to provide slide parts, the base metals of which are made of an aluminum alloy, and which are free from clearance variation even under temperature variations and excellent in abrasion-resistance and baking-resistance.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.